Abstract: In the present study, the floral morphology and development patterns of Impatiens longicornuta Y. L. Chen (Balsaminaceae) has been examined under the scanning electron microscope (SEM) for a better understanding of floral evolution in the genus. I.longicornuta is zygomorphic flower; lateral sepals 2; lower sepal deeply saccate, abruptly constricted into an incurved spur, mouth oblique, tip acuminate; upper petal cucullate, crista apically with a long cornu; stamens 5; ovary superior; gynoecium 5-carpellate, syncarpous. Initiation of five sepal primordial is not consistent in order. The order of initiation is from two lateral sepals to adaxial primordium and two anterolateral sepals. Their development is not synchronous also. The two anterolateral sepals stay rudimentary and disappear in later stages. The anterior petal arises firstly, and then the four lateral petal primordia are initiated in two successive pairs and fused at the base in later stages. Five stamen primordia initiate nearly at the same time. Five carpel primordia arise simultaneously in whorl. The perianth of Impatiens is pentamerous and the standard is not petal but sepal actually. The floral organogenesis data of I.longicornuta shows the important systematic and evolutional significance.

Key words: Impatiens L., floral organogenesis, Impatiens longicornuta, scanning electron microscopy